Tubular materials intended to be used as fuse casings, or fuse tubes, must meet a large number of requirements. They must be able to withstand the high pressures generated inside of fuses when blowing, to withstand without ageing significantly the temperatures prevailing in fuses while the latter are carrying current, be heat-shock resistant, be dimensionally stable, substantially non-tracking, cost-effective, etc. Some of the requirements under consideration can be met easily. There are, however, very few tubular materials which meet most or all requirements.
The basic art of pultrusion is known and has been applied to produce continual lengths of a variety of structures having quite dissimilar geometries, when viewed in cross-section, tubular structures are among these.
The tubular structures manufactured to date however, are not capable of withstanding the conditions to which electric fuses are subjected. In particular a high degree of heat-shock resistance and high bursting strength in excess of a few hundred PSI.
It is therefore the prime object of this invention to provide a method for making tubular structures of glass fiber reinforced synthetic resins that overcome the deficiencies of prior art pultruded tubing and lend themselves for use in electric fuses.
In particular the object of this invention is to provide a method for making tubular structures of glass fiber reinforced synthetic resins that have a high bursting strength and are more cost effective than prior art structures of this description.
Another object of this invention is to provide a novel pultrusion process that is cost effective and yields tubing having a high impact strength or dynamic strength.
Other objects of this invention will be apparent from what follows.